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As i915_gem_object_unbind() waits on an rcu_barrier() to flush vm releases (and destruction of their bound vma), we have to be careful not to invoke that barrier from beneath the shrinker: <4> [430.222671] WARNING: possible circular locking dependency detected <4> [430.222673] 5.4.0-rc8-CI-CI_DRM_7508+ #1 Tainted: G U <4> [430.222675] ------------------------------------------------------ <4> [430.222677] gem_pwrite/2317 is trying to acquire lock: <4> [430.222678] ffffffff82248218 (rcu_state.barrier_mutex){+.+.}, at: rcu_barrier+0x23/0x190 <4> [430.222685] but task is already holding lock: <4> [430.222687] ffffffff82263a40 (fs_reclaim){+.+.}, at: fs_reclaim_acquire.part.117+0x0/0x30 <4> [430.222691] which lock already depends on the new lock. <4> [430.222693] the existing dependency chain (in reverse order) is: <4> [430.222695] -> #2 (fs_reclaim){+.+.}: <4> [430.222698] fs_reclaim_acquire.part.117+0x24/0x30 <4> [430.222702] kmem_cache_alloc_trace+0x2a/0x2c0 <4> [430.222705] intel_cpuc_prepare+0x37/0x1a0 <4> [430.222709] cpuhp_invoke_callback+0x9b/0x9d0 <4> [430.222712] _cpu_up+0xa2/0x140 <4> [430.222714] do_cpu_up+0x61/0xa0 <4> [430.222718] smp_init+0x57/0x96 <4> [430.222722] kernel_init_freeable+0xac/0x1c7 <4> [430.222725] kernel_init+0x5/0x100 <4> [430.222728] ret_from_fork+0x24/0x50 <4> [430.222729] -> #1 (cpu_hotplug_lock.rw_sem){++++}: <4> [430.222733] cpus_read_lock+0x34/0xd0 <4> [430.222734] rcu_barrier+0xaa/0x190 <4> [430.222736] kernel_init+0x21/0x100 <4> [430.222737] ret_from_fork+0x24/0x50 <4> [430.222739] -> #0 (rcu_state.barrier_mutex){+.+.}: <4> [430.222742] __lock_acquire+0x1328/0x15d0 <4> [430.222743] lock_acquire+0xa7/0x1c0 <4> [430.222746] __mutex_lock+0x9a/0x9d0 <4> [430.222747] rcu_barrier+0x23/0x190 <4> [430.222850] i915_gem_object_unbind+0x264/0x3d0 [i915] <4> [430.222882] i915_gem_shrink+0x297/0x5f0 [i915] <4> [430.222912] i915_gem_shrink_all+0x38/0x60 [i915] <4> [430.222934] i915_drop_caches_set+0x1f0/0x240 [i915] <4> [430.222938] simple_attr_write+0xb0/0xd0 <4> [430.222941] full_proxy_write+0x51/0x80 <4> [430.222943] vfs_write+0xb9/0x1d0 <4> [430.222944] ksys_write+0x9f/0xe0 <4> [430.222946] do_syscall_64+0x4f/0x210 <4> [430.222948] entry_SYSCALL_64_after_hwframe+0x49/0xbe <4> [430.222950] other info that might help us debug this: <4> [430.222952] Chain exists of: rcu_state.barrier_mutex --> cpu_hotplug_lock.rw_sem --> fs_reclaim <4> [430.222955] Possible unsafe locking scenario: <4> [430.222957] CPU0 CPU1 <4> [430.222958] ---- ---- <4> [430.222960] lock(fs_reclaim); <4> [430.222961] lock(cpu_hotplug_lock.rw_sem); <4> [430.222963] lock(fs_reclaim); <4> [430.222964] lock(rcu_state.barrier_mutex); <4> [430.222966] *** DEADLOCK *** <4> [430.222968] 3 locks held by gem_pwrite/2317: <4> [430.222969] #0: ffff88849e2d9408 (sb_writers#14){.+.+}, at: vfs_write+0x1a4/0x1d0 <4> [430.222973] #1: ffff888496976db0 (&attr->mutex){+.+.}, at: simple_attr_write+0x36/0xd0 <4> [430.222976] #2: ffffffff82263a40 (fs_reclaim){+.+.}, at: fs_reclaim_acquire.part.117+0x0/0x30 <4> [430.222980] stack backtrace: <4> [430.222982] CPU: 1 PID: 2317 Comm: gem_pwrite Tainted: G U 5.4.0-rc8-CI-CI_DRM_7508+ #1 <4> [430.222985] Hardware name: Intel Corporation Tiger Lake Client Platform/TigerLake U DDR4 SODIMM RVP, BIOS TGLSFWI1.R00.2321.A08.1909162051 09/16/2019 <4> [430.222989] Call Trace: <4> [430.222992] dump_stack+0x71/0x9b <4> [430.222995] check_noncircular+0x19b/0x1c0 <4> [430.222998] ? __lock_acquire+0x1328/0x15d0 <4> [430.222999] __lock_acquire+0x1328/0x15d0 <4> [430.223001] ? mark_held_locks+0x49/0x70 <4> [430.223003] lock_acquire+0xa7/0x1c0 <4> [430.223005] ? rcu_barrier+0x23/0x190 <4> [430.223008] __mutex_lock+0x9a/0x9d0 <4> [430.223009] ? rcu_barrier+0x23/0x190 <4> [430.223011] ? rcu_barrier+0x23/0x190 <4> [430.223013] ? find_held_lock+0x2d/0x90 <4> [430.223045] ? i915_gem_object_unbind+0x24a/0x3d0 [i915] <4> [430.223048] ? rcu_barrier+0x23/0x190 <4> [430.223049] rcu_barrier+0x23/0x190 <4> [430.223081] i915_gem_object_unbind+0x264/0x3d0 [i915] <4> [430.223119] i915_gem_shrink+0x297/0x5f0 [i915] Closes: https://gitlab.freedesktop.org/drm/intel/issues/743 Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Matthew Auld <matthew.auld@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20191208161252.3015727-1-chris@chris-wilson.co.uk
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
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https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.